CC: Force push properties for all layers when tracing is started

cc/trees/layer_tree_host.cc

 // Copyright 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "cc/trees/layer_tree_host.h"
 
 #include <algorithm>
 #include <stack>
 #include <string>
 
 #include "base/atomic_sequence_num.h"
 #include "base/bind.h"
 #include "base/command_line.h"
 #include "base/message_loop/message_loop.h"
 #include "base/metrics/histogram.h"
 #include "base/stl_util.h"
 #include "base/strings/string_number_conversions.h"
 #include "base/trace_event/trace_event.h"
 #include "base/trace_event/trace_event_argument.h"
 #include "cc/animation/animation_registrar.h"
 #include "cc/animation/layer_animation_controller.h"
 #include "cc/base/math_util.h"
 #include "cc/debug/devtools_instrumentation.h"
+#include "cc/debug/frame_viewer_instrumentation.h"
 #include "cc/debug/rendering_stats_instrumentation.h"
 #include "cc/input/layer_selection_bound.h"
 #include "cc/input/page_scale_animation.h"
 #include "cc/input/top_controls_manager.h"
 #include "cc/layers/heads_up_display_layer.h"
 #include "cc/layers/heads_up_display_layer_impl.h"
 #include "cc/layers/layer.h"
 #include "cc/layers/layer_iterator.h"
 #include "cc/layers/painted_scrollbar_layer.h"
 #include "cc/layers/render_surface.h"
@@ skipping 227 matching lines @@
     }
 
     host_impl->set_max_memory_needed_bytes(
         contents_texture_manager_->MaxMemoryNeededBytes());
 
     contents_texture_manager_->UpdateBackingsState(
         host_impl->resource_provider());
     contents_texture_manager_->ReduceMemory(host_impl->resource_provider());
   }
 
+  bool is_new_trace;
+  TRACE_EVENT_IS_NEW_TRACE(&is_new_trace);
+  if (is_new_trace &&

[danakj, 2015/03/17 17:08:53]

I think you need if (root_layer()) as well here.

[caseq, 2015/03/17 17:44:55]

Thanks, done!
FWIW we seem to unconditionally arrive to a call to
TreeSynchronizer::PushProperties() at the end which does a DCHECK() on its
source root layer (sure, there's still pretty important difference in case of
release :))

[danakj, 2015/03/17 18:36:05]

I think it does an early out:
https://code.google.com/p/chromium/codesearch#chromium/src/cc/trees/tree_sync...

We can definitely commit without a root layer.

+      frame_viewer_instrumentation::IsTracingLayerTreeSnapshots()) {
+    LayerTreeHostCommon::CallFunctionForSubtree(
+        root_layer(), [](Layer* layer) { layer->DidBeginTracing(); });
+  }
+
   LayerTreeImpl* sync_tree = host_impl->sync_tree();
 
   if (next_commit_forces_redraw_) {
     sync_tree->ForceRedrawNextActivation();
     next_commit_forces_redraw_ = false;
   }
 
   sync_tree->set_source_frame_number(source_frame_number());
 
   if (needs_full_tree_sync_) {
@@ skipping 973 matching lines @@
     bool children_need_begin_frames) const {
   proxy_->SetChildrenNeedBeginFrames(children_need_begin_frames);
 }
 
 void LayerTreeHost::SendBeginFramesToChildren(
     const BeginFrameArgs& args) const {
   client_->SendBeginFramesToChildren(args);
 }
 
 }  // namespace cc